Energy efficiency plus more reasons to build a prefab house

The prefab component of this 3,851-square-foot house in Austin is the structurally insulated panels used for its building envelope. (Courtesy of Alison Cartwright)

Author Sheri Koones is on a mission to educate American homeowners about home building.

Her first three books focused on the basics on home construction, borne of her own experience as a frustrated homeowner trying to remodel her Greenwich, Conn., house. At that time, she said in a recent interview, there was almost no information to help her make intelligent choices as she faced an endless number of decisions about this or that flooring material, plumbing fixture, roof shingle and on and on.

Koones' last four books have zeroed in on prefabricated, factory-built housing. For more than 100 years, this type of housing has been promoted by designers and entrepreneurs who have touted its efficiency, speed and affordability, but with limited success. It remains a niche market, and most homeowners still equate prefabrication and modular housing with trailers, Koones said. She wants to set them straight.

With "Prefabulous + Almost Off the Grid: Your Path to Building an Energy- Independent Home," (Abrams, $25), Koones presents a wide variety of prefab houses. A "modular" prefab house is constructed in sections in a factory, transported on flatbed trucks and joined together at the building site.

The 32 prefab houses that Koones features in her book show that the aesthetics of prefab housing are as varied as the different types of prefabrication. Stylistically, these houses run the gamut from strictly traditional to starkly contemporary, and they all feature inviting, light-filled interiors. No one will mistake them for trailers. The 32 houses were built in both urban and rural areas. By current standards, they are modest in size; more than half of them have less than 2,500 square feet of living space.

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The owners gravitated to prefab, Koones said, because they determined that it was the best way to build a new house that would be unusually energy-efficient and easy to maintain.

Koones offers additional reasons to build a prefab house. For her, one of the most important will surprise homeowners who are not familiar with the construction process. A factory-built house minimizes waste; most site-built houses fill up a dumpster several times over. Factories, where the same house parts are assembled over and over, can more accurately predict what they will need so that waste is minimized.

A second plus with a prefab house is its speed of construction. While a site-built house takes about four to 15 months to complete, a prefab generally takes weeks. Because most of the work is done in a factory, there are no weather delays and no damage to exposed framing when it is deluged in a summer thunderstorm. Perhaps most importantly for owners, speeding up the construction process reduces the amount of stress that most endure as their house goes up.

Koones says that prefab houses are built with higher quality control than site-built ones. In many factories now, the workers use sophisticated, computer-aided machinery that makes more accurate cuts so that the framing pieces fit together more easily; this in turn makes all the subsequent steps in the construction sequence, including the installation of interior and exterior materials and windows, faster and easier.

The cover of Sheri Koones' new book "Prefabulous Almost Off the Grid"; Koones is on a mission to educate Americans about home building. (Courtesy of Trent Bell)

All the houses in Koones' book were custom-built. But given the advantages of factory production, especially in creating energy-efficient houses, could an entire subdivision be built this way, especially as energy code requirements ratchet upward? Daniel Gainsboro of Now Communities, a Boston home-building firm whose work will be featured in Koones' next book, is planning to do exactly that, using the Bensonwood Homes wall system featured in the "Unity House" described in her current book.

In the past, production builders have eschewed prefab, saying that it costs too much. Gainsboro opted for prefab for the opposite reason. The system he is using is a faster, more efficient and less costly way to build the 12-inch thick walls that he is using to make his houses 60 percent more energy-efficient than conventionally built ones in the Boston area.

When he built the cumbersome, multi-layered walls on site, his crews found it frustrating and time-consuming. What took them three weeks, Bensonwood can do in 2 1/2 days. Another plus: Bensonwood's computerized production system allows Gainsboro to tweak the amount of insulation in each wall, depending on its orientation and sun exposure, a degree of fine-tuning that the builder of a site-built house can only dream about.

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Katherine Salant has an architecture degree from Harvard. A native Washingtonian, she grew up in Fairfax County, Va., and now lives in Ann Arbor, Mich. If you have questions or column ideas, she can be contacted at salanthousewatch@gmail.com orwww.katherinesalant.com.